ESCO Brazing and Soldering Practice Test

Cleaning the workpieces with a wire brush or sand cloth is essential because solder only wets clean metal surfaces. Oxide films, oils, and dirt form quickly and block bonding, so scrubbing them away exposes fresh metal for the flux and solder to act on. This improves wetting and allows capillary action to draw the solder into the joint, producing a stronger, reliable connection. If you skip this cleaning or replace it with just wiping, soaking in water, or preheating before cleaning, contaminants and moisture can prevent proper bonding and lead to a weak joint. After cleaning, apply flux and then heat to assist oxide removal and wetting during soldering.